The present invention pertains to materials and a method of producing the materials for use in encapsulation of electronic components and the like which are to be utilized in high acceleration and high thermal cycling environments. Also, the materials may be used for other energy absorbtive means. In high acceleration and high thermal cyclying environments, the thermal expansion coefficients of electronic components and encapsulating materials differ. Therefore, a foam is needed which will not apply thermal expansion stress to the electronic components which are encapsulated so that the electronic circuitry is not rendered ineffective.
Typically, foams used for encapsulation of electronic components in high acceleration and high thermal cycling environments are chemically blown or mechanically frothed possibly requiring toxic chemical blowing agents such as freon, self stabilizer chemicals or cabon dioxide (CO.sub.2) reactions. In such environments, solid polyurethane formulations tend to cause stress damage. Also, solid polyurethane formulations do not sufficiently re-expand after they are compressed. In addition, chemically foaming polyurethane is an extremely difficult process to control.
Methods such as mixing air bubbles or hollow glass microspheres into an uncured, thermosetting resin are well known in the art. However, a material is needed which cures at a temperature and pressure so as not to damage the encapsulated electronic components, has better re-expansion properties and can be more flexible.